With typical spinning reels, the drag is normally set at about 1/3  the breaking strength of the line. This allows for enough pressure to set the hook and keep the quick start up pressure at less than the breaking strength of the line. As a fish makes a run, the drag lets the spool unwind at a set pressure to avoid breaking the line. The angler does not have to be alert or react for the drag to work.
Generally, a spinning reel is provided at a front part of a spool with a drag mechanism which is adapted to control the paying out of fishing line due to reversing of the spool in accordance with the pulling force of the fish. This drag mechanism, mounted on the spool, however, poses problems that may cause the fishing line to be twisted.
In order to overcome these problems, it has been proposed to mount a drag mechanism at a rear part of a rotor, as shown in Japanese Utility Model Laid-Open Application No. 132888/1977. However, the adjustment of the braking force is difficult during the taking up of the fishing line because the manipulation knob of the drag mechanism is rotating during operation of the drag mechanism.
The drag mechanism, including a braking disc, braking member and manipulation knob, is rotated as a unit with the rotor to impart an unnecessarily large inertia to the rotor so as to hinder the swift manipulation of the handle. In addition, since the manipulation knob has to be installed between the housing and the rotor, the length of the reel in the axial direction of the spool is increased, resulting not only in an increase of a size of the reel but also in a rough adjusting operation.
In order to overcome these problems, U.S. Pat. No. 4,416,427 has a drag mechanism of a one way engagement type which engages the rotor only when the rotor is reversed. The drag adjustment knob is mounted at the back of the housing. The reason for this is because U.S. Pat. No. 4,416,427 relates to a spinning reel of a skirted spool type.
The inherent problems with having rotor drag on a skirted spool spinning reel are (1) the rotor has protrusions (bail, bail arms, bail closing mechanism, etc.) which eliminate a possibility of manually palming the rotor for increased drag, (2) protrusions are likely to strike the angler's fingers during rapid fish runs, and (3) putting the drag adjustment knob on the back of the housing increases the bulk and weight of the reel, increases the number of parts in the reel and creates a place where line can become entangled. Furthermore, the spinning reel of U.S. Pat. No. 4,416,427 incorporates engaging claws to engage drag discs with the rotor. This is not an instantly engaging mechanism, which means there will be a good bit of free backward rotor rotation before the claws engage, creating loose line and a hesitation before hook sets. Loose line coupled with twisted line creates most of the line tangling problems associated with spinning reels. It is also difficult to seal this mechanism from contaminates.
Furthermore, the spinning reel of U.S. Pat. No. 4,416,427 requires additional parts for locking the rotor for storage.